It appears you've replaced all the capacitors in the middle of the board in post 353 vs. the ones in the original BOM and the picture in post 99.

You only mentioned the change to C1 as being an improvement. How did the change to the others affect anything, if any? What parts did you use in the changes?

Did you change any in the power supply board?

Keep the recommended changes, only C1 plus some small series resistor. I did a lot of experiments in order to find a lucky cap combination ... so I've spend a lot of money almost for nothing and I succeed to destroy a some boards by desoldering and resoldering components .
The only caps, besides C1, which might probably worth to be changed are in power supply (MUSE KG)

Hello and Happy new Year !
Very sexy design! Congratulations Roender !
I copy the ltspice file (ltspice installed and used for the first time) .
I can't simulate because : "Multiple instances of "Flag" "
Do you know what can i do ?
Thank you !